Process for the continuous steam treatment of staple fiber

ABSTRACT

A process and apparatus for the continuous steam treatment of staple fiber which comprises a steamtight housing provided with heating means, said housing containing a heating zone and a dwell zone, sieve means rotatably disposed in the heating zone, steam distribution means associated with the surface of the sieve means, inlet means for introducing the fiber onto the sieve means, conveyor belt means disposed in the heating zone below the sieve means and extending through the dwell zone and at least one sieve means disposed behind the steamtight housing at its outlet end.

United States Patent [1 1 Fleissner [4 1 Nov. 6, 1973 1 PROCESS FOR THE CONTINUOUS STEAM TREATMENT OF STAPLE FIBER [75] Inventor: Heinz Fleissner, Frankfurt am Main,

Germany [73] Assignee: VEPA AG, Basel/Schweiz, Germany [22] Filed: Feb. 22, 1971 [21] Appl. No.: 117,481

[30] Foreign Application Priority Data Feb. 21, 1970 Germany P 20 08 079.9

Mar. 28, 1970 Germany P 20 15 041.8

[52] US. Cl 8/1493, 26/185, 68/DIG. 5, I 68/5 D [51] Int. Cl. D06c l/06 [58] Field of'Search 8/1493; 68/DIG. 5,

68/5 R, 5 D, 5 E, l9, 19.1; 26/185 [56] I References Cited UNITED STATES PATENTS Speers 68/5 D 3,222,895 12/1965 Sheppard 68/5 D 3,503,231 3/1970 Fleissner et al. 68/5 E 3,529,447 9/1970 Fleissner et al' 68/D1G. 5

FOREIGN PATENTS OR APPLICATIONS 1,195,916 6/1970 Great Britain 68/DlG. 5

'Primary Examiner-John Petrakes Assistant Examiner-Philip R. Coe

. Att0rneyCraig, Antonelli, Stewart & Hill [57] ABSTRACT A process and apparatus for the continuous steam treatment of staple fiber which comprises a steamtight housing provided with heating means, said housing containing a heating zone and a dwell zone, sieve means rotatably disposed in the heating zone, steam distribution means associated with the surface of the sieve means, inlet means for introducing the fiber onto the sieve means, conveyor belt means disposed in the heating zone below the sieve means and extending through the dwell zone and at least one sieve means disposed behind the steamtight housing at its outlet end.

9 Claims, 4 Drawing Figures PATENTEUHUK/ 01975 3,770 374 SHEET 16F 2 In ventor HEINY. FLEISSNER BY Craig, Ankmeui, Stewart 1 H1 ATT RNEYS PATENTEDHHY ems 3,770,374

SHEET REF 2 Fig. L

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HEINZ FLEISSNER BY CIO IS Antaneul, Stewart ATTORNEYS PROCESS FOR Til-IE CONTINUOUS STEAM TREATMENT'OF STAPLE FIBER BACKGROUND OF THE INVENTION The present invention relates to a process for the continuous steaming of staple fibers, especially for the shrinking of synthetic fibers, preferably polyacrylonitrilic fibers. The process is effected by rapid heating a fibrous web disposed on a sieve by drawing steam therethrough, by permitting the web to subsequently dwell in a steam atmosphere for a certain period of time and finally by removing the steam from the web.

The process which can be carried out on the apparatus described and claimed in previous patent applications' of the present inventor is'advantageous because it permits the continuous steam treatment of the fibers in the form of fabrics, knitted fabrics, endless tows or webs. The rapid heating-up of the material to be treated in the first section of the belt steamer is advantageous because the shock-like heating-up eliminates any danger of the steam condensing on the cold material entering the apparatus. To this end, the feeding unit operates at a'higher speed than the subsequent sieve belt on which the textile material slowly passes through the dwell zone, for example, in a plaited condition.

Such belt steamer can also be used for shrinking synthetic fibers. Investigations have shown that low residual shrinking values can be obtained only on condition that the fibers are treated by means of oversaturated steam. As a consequence, there are devices required forsuperheating the saturated steam which has been produced in the water sump. However, it is also possible to use steam which has been produced outside the apparatus. In any case, the test results wereonly satisfying when the steam was heated to approximately 115 to 125C. and when the steam was very turbulently circulated in the treatment chamber. It is obvious that such a steam treatment is very effective with a strong steam vorticity because a strong movement of the processing medium ensures a repeated contact between other than water, e.g., by drawing the steam out of the fibrous web.

Apart from the necessity of obtaining low residual shrinking values in an economical way, it has always been an objection that on leaving the steamer the fibrous material is too wet. Usually the initial moisture content is about 5 to 6 per cent. This moisture content increases in the steamer, and more with saturated steam than with superheated steam. Saturated steam, on the other hand, ensures a more thorough wetting and as a consequence the more rapid heating-up of the fibers so that the apparatus can have a shorter overall length while having the same production capacity as longer apparatus. In any case, the final moisture content is 10 to 11 per cent. It can be decreased to the value of the initial content by drawing the steam out of the treated material and simultaneously cooling the fibrous web. If this lower final moisture content is still too high the fibers must be dried in a dryer. To this end, it is recommended to render the web, which is rather voluminous while passing through the steamer, thinner before feeding it into the dryer.

The devi'cefor carrying out the above process is an essentially known sieve belt steamer. The sieve belt of the steamer passes the steaming compartment in the longitudinal direction and the intake end of the sieve belt is preceded by a feeding unit. In contrast to other steamers which are claimed to be advantageous for other processes, this type of steamer must feature a dwell zone which is absolutely air-free and where there is no forced movement of the steam. It is generally known that air has a higher specific weight than steam. As a consequence, any air in the steamer will gather on the floor of the apparatus and will not impede the steaming process. The steam which rises from the water sump flows over and through the material lying absolutely tension-free on the sieve belt solely by its upward the fibers and the steam particles. It has been found advantageous to equip the outlet end of thesteamer with a water curtain which permits the continuous delivery of the fibrous material without any steam losses. However, this arrangement is disadvantageous in so far as the fibrous material is one hundred percent wetted and that this moisture must be subsequently removed.

On principle, the above described process and the required apparatus are advantageous but the power consumption caused by the absolutely necessary overheating of the steam is very high. Experimentation has SUMMARY OF THE INVENTION According to the present invention this is achieved by letting the fibers pass a calm and absolutely air-free saturated steam atmosphere in the dwell zone, without any tension, and by subsequently removing the steam which rests on or among the fibers by another means movement, which is conditional on physical laws. This is the only way to obtain final shrinking values of less than 1 percent by means of saturated steam, and this is obtained with fibers, the shrinkage value of which is 10 percent at the beginning of the treatment process.

The staple fibers to be shrunk lies on the conveyor belt in form of a random web and shrinks under the influence of the steam. The conveyor belt, usually installed in such a steamer, is a wire mesh belt of VA stainless steel, i.e., a fabric of fine steel wires. Compared with link belts which are very susceptible to wear because of the constant bending of links, wire mesh belts and more advantageous because of the steel wire mesh is resistant to mechanical strain. There is the one drawback, however, that a certain amount of fibers cling to the wires, especially at the points of intersection and thus obstruct the wire meshes and impede the steam flow and the penetration of the steam through v the web in a given treatment period.

This problem of eliminating any danger of fibers obstructing the endless conveyor belt and ensuring the uniform steam penetration, even for a prolonged period of time, can best be solved by replacing the wire mesh belt by a jointless perforated belt which can be In principle, it is known to arrange a sieve drum in the heating-up section of the belt steamer, said sieve drum utilized for taking the web up and feeding it into the proper heating section. It is'advantageous to form the web on this sieve drum instead of feeding the fibers, already in the form of a web, onto said drum. According to the present invention, this can be done by providing at least part of the suction area of this sieve drum or another sieve drum which may precede the latter and be connected with it by a transporting element, with a trumpet-shaped pipe through which the individual fibers are pneumatically fed onto the drum. The end of this pipe which faces the sieve drum embraces that drum section which is not screened by the baffle inside the drum.

The fibers which are transported forth by means of a compressed-air stream adhere to the sieve drum because of the suction draft prevailing on the drum. The fibers are rapidly heated and transported towards and transferred onto the sieve belt which is arranged underneath the drum.

It is also feasible to provide an endless sieve inlet conveyor and to arrange a suction fan underneath the front part of the carrying stringer of this conveyor and to put the wide end of the trumpet-shaped pipe for the pneumatic feeding of the fibers over this fan. This arrangement is attractive because of the relatively low production costs it requires, and because it has the same effect as the aforementioned. I

The heating-up process can be rendered more effective by adjoining either to the seive drum or the endless belt in the heating section a steam spraying arrangement which faces the web. This would ensurethat the steam is directly applied to the web, not only by the suction draft of.the sieve drum.

In contrast to other steamers, the outlet ends of which are provided with water curtains, this belt steamer comprises an exhaust assembly for removing the steam from the web. This steam removing assembly can consist of exhaust devices, e.g., fans which are arranged above or underneath the carrying stringer of the sieve belt, and outside and behind the treatment chamber. Another possibility consists in providing one or several cooling drums following the sieve belt, said cooling drums taking the web off the belt and on which, the web is intensively penetrated by cold air'.

Especially in those cases where the web is to be dried after the steaming process, it is of advantage to reduce its thickness. This can be done by means of a carding cylinder which feeds the thinner web onto an endless conveyor leading to the subsequent drying unit.

DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only and thus are not limitative of the present invention and wherein,

FIG. 1 is a longitudinal section through a belt steamer comprising a fiber feeding unit at its inlet end and a delivery unit, said steamer being followed by a dryer; and

FIG. 4 is an enlargened view of part of the endless belt of the steamer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The belt steamer as shown in FIGS. 1-3 comprises a steam-tight and heat insulated housing 1 through which a steam-permeable endless conveyor belt 2 is guided. The conveyor belt 2 projects outside the steaming compartment at the outlet end 3 of the steamer. The belt 2 is a jointless steel or plastic belt with punched-out perforation holes. On the floor of the steamer housing 1 there are installed water-covered heating batteries 4 which produce the saturated steam for treating the material. At the ceiling of the belt steamer heating rods 5 are also arranged which eliminate any condensate formation.

At the inlet end of the belt steamer, above the sieve belt 2, a sieve drum 6 is arranged which, according to FIG. 1, is embraced by a conveyor belt 8 which projects to the outside at the front side of the steamer. The upper stringer of the conveyor belt carries a thin fibrous web 7. The web 7 is formed on the sieve drum 9 preceding the sieve drum 6. The fibers are guided pneumatically through a trumpet-shaped pipe 10 and introduced onto the suction area of the sieve drum 9 from where they are then continuously transferred onto the subsequent conveyor belt in form of a web 7. The thin fibrous web 7 is rapidly heated up on the sieve drum 6 and then taken over by the sieve belt 2 where it is plaited or piled up to form thickned web 13.

The dwell zone following the heating section of the belt steamer features a completely air-free and calm steam atmosphere. The steam flows through the fibers which lie absolutely tension-free on the sieve belt, thereby causing them to shrink.

Subsequent to the steam treatment the steam has to be removed from the fibrous web. With the device according to FIG. 1 this is achieved by means of two sieve drums 11 and 12 which are arranged one above the other and which draw in fresh ambient air. On these drums the fibrous web 19 arriving from the belt 2 is subjected to an intensive cooling process. At the same time the drying process begins. The drying process generally does not have to be very intensive because on leaving the steamer the web has a final moisture content of only about 10 to 11 percent. From the sieve drum 12 the fibers are fed into a funnel 14 which guides them to a baling press (not shown).

However, if the web is to be dried to less than its initial moisture content of approximately 5 percent, the steamer must be followed by a dryer (see FIG. 3). Before being dried the web ought to be rendered thinner. To this end, a carding roller 17 is arranged at the outlet end of the belt 2. The subsequent conveyor 18 then feeds the thin web 19 into the dryer 20, at an elevated speed. The conveyor is equipped with lateral walls 21 so that there is a channel for the thin web produced.

The embodiment of the present invention shown in FIG. 2 corresponds to that shown in FIG. 1, the only difference being that the sieve drum 9 preceding the sievedrum 6 as well as the conveyor 8 embracing the sieve drum 6 have been omitted.

The fibrous web is in this case formed on the sieve drum 6 by means of the trumpet-shaped pipe 10. Be-

fore falling down onto the sieve belt the web can be intensively sprayed with steam by means of the steam spray pipe which faces the sieve drum. This steam application ensures the shock-like heating-up of the web right at the beginning of the steaming process. At the rear end of the belt 2 as shown in FIG. 2 there are fans 16 installed underneath the carrying stringer of the belt. These fans draw in fresh ambient air and exhaust the steam to the outside, between the carrying stringer and the return stringer of the belt. The steam is thus removed from the web which is simultaneously cooled. The embodiment of the device which is shown in FIG. 3 does not comprise any sieve drum at its inlet end. In this case the web 7 is formed on the ingoing sieve belt 22 by means of the suction fan 23.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be apparent to one skilled in the art are intended to be included.

I claim:

1. A process for the continuous steam treatment of staple fiber which comprises forming stable fibers into a fibrous web, conveying the fibrous web on a sieve means into a steam chamber, rapidly heating the fibrous web by drawing steam therethrough as the web is conveyed on said sieve means, conveying the fibrous web, without tension, through an air-free saturated steam atmosphere, permitting the steam to dwell for a period of time in said steam atmosphere to effect shrinkage of the fibrous web, removing the fibrous web from the steam chamber and removing the steam from the fibers of said web without the web coming in contact with water by passing air through said fibrous web.

2. The process of claim 1 wherein said staple fibers are synthetic fibers.

3. The process of claim 1 wherein the fibrous web is cooled while the steam is being removed therefrom.

4. The process of claim 1 wherein the fibrous web is dried after being steam treated.

5. The process of claim 4 wherein the thick fibrous web which is removed from the steam atmosphere is rendered thinner before being subjected to the subsequent drying step.

6. The process of claim 1 wherein the steam is removed from said fibrous web by passing the fibrous web over a sieve drum means subjected to a suction draft and by drawing air through said fibrous web.

7. The process of claim 6 wherein the fibrous web is made of polyacrylonitrile fibers.

8. The process of claim 1, wherein the steam is removed from the fibrous web by passing fresh, ambient air through the web.

9. The process of claim 1 wherein the steam is removed from said fibrous web by conveying the fibrous web on sieve means and by drawing air through the fibrous web and through the sieve means. 

2. The process of claim 1 wherein said staple fibers are synthetic fibers.
 3. The process of claim 1 wherein the fibrous web is cooled while the steam is being removed therefrom.
 4. The process of claim 1 wherein the fibrous web is dried after being steam treated.
 5. The process of claim 4 wherein the thick fibrous web which is removed from the steam atmosphere is rendered thinner before being subjected to the subsequent drying step.
 6. The process of claim 1 wherein the steam is removed from said fibrous web by passing the fibrous web over a sieve drum means subjected to a suction draft and by drawing air through said fibrous web.
 7. The process of claim 6 wherein the fibrous web is made of polyacrylonitrile fibers.
 8. The process of claim 1, wherein the steam is removed from the fibrous web by passing fresh, ambient air through the web.
 9. The process of claim 1 wherein the steam is removed from said fibrous web by conveying the fibrous web on sieve means and by drawing air through the fibrous web and through the sieve means. 